For a number or reasons, layers of insulating materials in the form of e.g. sheets of mineral wool, instead of being glued to the underlying layer or substratum which may consist of profiled sheet metal, are nowadays more often attached to the support with the aid of washers and screws. The work of securing sheets of this kind with the aid of washers and screws is, however, a tedious and time-consuming one as the workman must stoop down and deposit the washers along a demarkation line and thereafter tighten the screws, which in turn requires the use of some kind of tool which is moved into engagement with the screw heads.